Simultaneous sensing arrangement

ABSTRACT

Multi-touch touch-sensing devices and methods are described herein. The touch sensing devices can include multiple sense points, each located at a crossing of a drive line and a sense line. In some embodiments, multiple drive lines may be simultaneously or nearly simultaneously stimulated with drive signals having unique characteristics, such as phase or frequency. A sense signal can occur on each sense line that can be related to the drive signals by an amount of touch present at sense points corresponding to the stimulated drive lines and the sense line. By using processing techniques based on the unique drive signals, an amount of touch corresponding to each sense point can be extracted from the sense signal. The touch sensing methods and devices can be incorporated into interfaces for a variety of electronic devices such as a desktop, tablet, notebook, and handheld computers, personal digital assistants, media players, and mobile telephones.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/380,747, filed Dec. 15, 2016 and published on Apr. 6, 2017 as U.S.Publication No. 2017-0097728, which is continuation of U.S. patentapplication Ser. No. 14/482,979, filed Sep. 10, 2014, now U.S. Pat. No.9,552,115, issued Jan. 24, 2017, which is a continuation of U.S. patentapplication Ser. No. 14/019,264, filed Sep. 5, 2013, now U.S. Pat. No.8,928,617, issued Jan. 6, 2015, which is a continuation of U.S. patentapplication Ser. No. 12/874,184, filed Sep. 1, 2010, now U.S. Pat. No.8,552,998, issued Oct. 8, 2013, which is a division of U.S. patentapplication Ser. No. 11/619,433, filed Jan. 3, 2007, now U.S. Pat. No.7,812,827, issued Oct. 12, 2010, the entire disclosures of which arealso incorporated herein by reference. The present application is alsorelated to the following U.S. Patents and Patent Applications, each ofwhich is hereby incorporated by reference in its entirety:

-   -   U.S. patent application Ser. No. 09/236,513, titled “Method and        Apparatus for Integrating Manual Input,” filed Jan. 25, 1999,        now U.S. Pat. No. 6,323,846, issued Nov. 27, 2001;    -   U.S. patent application Ser. No. 10/840,862, titled “Multipoint        Touchscreen,” filed May 6, 2004, now U.S. Pat. No. 7,663,607,        issued Feb. 16, 2010; and    -   U.S. patent application Ser. No. 11/381,313, titled “Multipoint        Touch Surface Controller,” filed May 2, 2006, now U.S. Pat. No.        8,279,180, issued Oct. 2, 2012.

BACKGROUND

Recently, interest has developed in touch and/or proximity-based inputsystems for electronic devices and computer systems that are capable ofrecognizing multiple touch and/or hover events simultaneously. Many ofthese systems, for example those based on mutual capacitance or certainoptical sensing arrangements, involve applying periodic stimuluswaveforms to a plurality of sense points and detecting sense waveformsthat can be related to the periodic stimulus waveform by the amount oftouch and/or proximity present at the sense point. In some embodiments,these systems apply periodic stimulus waveforms to drive lines that arecoupled to sense lines at the sense points. Typically, stimuluswaveforms have been applied to these drive lines one at a time. Becausedevices typically include a plurality of these drive lines, each driveline has been driven sequentially.

SUMMARY

According to one embodiment of the invention, a method of deriving touchinformation from a touch sensitive surface is provided. The touchsensitive device can include a plurality of sensing points. Each sensingpoint can be located at or near a crossing of a drive line and a senseline. For example, the method can include simultaneously (orsubstantially simultaneously) stimulating a plurality of the drive lineswith one or more unique drive signals. For example, the signals may havepredetermined phase and/or frequency relationships. The method canfurther include sensing a sense signal on at least one of the senselines. The sense signal can relate to the drive signals by touch orproximity of one or more objects to one or more sensing points locatedat or near the crossing of the plurality of drive lines and the at leastone sense line. The method can also include, for example, deriving touchinformation from the sense signal. Touch may be derived from the sensesignal by deriving a plurality of values from the sense signal, e.g., byintegrating the sense signal over one or more time periods and derivingtouch information from a mathematical combination of the plurality ofvalues.

In another embodiment, the invention can relate to a multi-touch sensingdevice. The touch sensing device can include, for example, a touchsensitive surface with a plurality of sensing points located at acrossings of drive lines and sense lines. The touch sensing device canalso include drive circuitry configured to simultaneously apply uniquedrive signals to a plurality of the drive lines. For example, thesignals may have predetermined phase and/or frequency relationships. Thetouch sensing device can also include sense circuitry that is configuredto detect a sense signal in at least one sense line and derive touchinformation from this sense signal for one or more of the sense points.Such a touch sensing device may be based, for example, on self or mutualcapacitance.

In yet another embodiment, the invention can relate to an electronicdevice or computer system incorporating a touch sensing arrangement orimplementing a touch sensing method, as discussed above. The electronicdevice can take a variety of forms, including, for example, a desktopcomputer, a tablet computer, a notebook computer, a handheld computer, apersonal digital assistant, a media player, or a mobile telephone. Otherform factors are also possible.

In still another embodiment, the present invention can relate to amethod of deriving touch information from a touch sensitive surface. Themethod can include performing a coarse scan of a region of the touchsensitive surface to determine whether a touch is present within thefirst region. If a touch is present, fine scanning of the region may beperformed to determine more exact data about the touch or touches thatare present within the region. If a touch is not present, fine scanningany be omitted, and a coarse scan of another region may begin. Byeliminating unnecessary fine scans, time and power savings can result.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned and other aspects of the invention may best beunderstood by reference to the following description taken inconjunction with the accompanying drawings in which:

FIG. 1 illustrates a multi-touch sensing device used as an input deviceto a computer system in accordance with an embodiment of the presentinvention.

FIG. 2 illustrates a plurality of contact patch areas corresponding toan object in proximity to a plurality of sense points of a multi-touchsurface in accordance with an embodiment of the present invention.

FIG. 3 illustrates a simplified schematic diagram of a mutualcapacitance sensing circuit that may be used in an embodiment of thepresent invention.

FIG. 4 illustrates a process for operating a multi-touch sensing devicein accordance with an embodiment of the present invention.

FIG. 5 illustrates a multi-touch sensing device in accordance with anembodiment of the present invention.

FIG. 6 illustrates a process for performing multi-line stimulation inaccordance with an embodiment of the present invention.

FIG. 7 illustrates a single-line stimulation arrangement according tothe prior art.

FIG. 8 illustrates a two-line simultaneous stimulation arrangement inaccordance with an embodiment of the present invention.

FIG. 9 illustrates a four-line simultaneous stimulation arrangement inaccordance with an embodiment of the present invention.

FIG. 10 illustrates a variety of electronic device and computer systemform factors that may be used in accordance with an embodiment of thepresent invention.

FIG. 11 illustrates a frequency-based four-line simultaneous stimulationarrangement in accordance with an embodiment of the present invention.

FIGS. 12A-E illustrate generally various alternatives for stimuluswindows in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Recognizing multiple simultaneous or near-simultaneous touch events maybe accomplished with a multi-touch sensing arrangement as illustrated inFIG. 1 . Multi-touch sensing arrangement 100 can detect and monitormultiple touch attributes (including, for example, identification,position, velocity, size, shape, and magnitude) across touch sensitivesurface 101, at the same time, nearly the same time, at different times,or over a period of time. Touch sensitive surface 101 can provide aplurality of sensor points, coordinates, or nodes 102 that functionsubstantially independently of one another and that represent differentpoints on a touch sensitive surface. Sensing points 102 may bepositioned in a grid or a pixel array, with each sensing point capableof generating a signal at the same time. Sensing points 102 may beconsidered as mapping touch sensitive surface 101 into a coordinatesystem, for example, a Cartesian or polar coordinate system.

A touch sensitive surface may, for example, be in the form of a tabletor a touch screen. To produce a touch screen, the capacitance sensingpoints and other associated electrical structures can be formed with asubstantially transparent conductive medium, such as indium tin oxide(ITO). The number and configuration of sensing points 102 may be varied.The number of sensing points 102 generally depends on the desiredresolution and sensitivity. In touch-screen applications, the number ofsensing points 102 may also depend on the desired transparency of thetouch screen.

Using a multi-touch sensing arrangement, like that described in greaterdetail below, signals generated at nodes 102 of multi-touch sensor 101may be used to produce an image of the touches at a particular point intime. For example, each object (e.g., finger, stylus, etc.) in contactwith or in proximity to touch sensitive surface 101 can produce contactpatch area 201, as illustrated in FIG. 2 . Each of contact patch area201 may cover several nodes 102. Covered nodes 202 may detect theobject, while remaining nodes 102 do not. As a result, a pixilated imageof the touch surface plane (which may be referred to as a touch image, amulti-touch image, or a proximity image) can be formed. The signals foreach contact patch area 201 may be grouped together. Each contact patcharea 201 may include high and low points based on the amount of touch ateach point. The shape of contact patch area 201, as well as the high andlow points within the image, may be used to differentiate contact patchareas 201 that are in close proximity to one another. Furthermore, thecurrent image can be compared to previous images to determine how theobjects may be moving over time, and what corresponding action should beperformed in a host device as a result thereof.

Many different sensing technologies can be used in conjunction withthese sensing arrangements, including resistive, capacitive, optical,etc. In capacitance-based sensing arrangements, as an object approachestouch-sensitive surface 101, a small capacitance forms between theobject and sensing points 102 in proximity to the object. By detectingchanges in capacitance at each of the sensing points 102 caused by thissmall capacitance, and by noting the position of the sensing points, asensing circuit 103 can detect and monitor multiple touches. Thecapacitive sensing nodes may be based on self capacitance or mutualcapacitance.

In self capacitance systems, the “self” capacitance of a sensing pointis measured relative to some reference, e.g., ground. Sensing points 102may be spatially separated electrodes. These electrodes are coupled todriving circuitry 104 and sensing circuitry 103 by conductive traces 105a (drive lines) and 105 b (sense lines). In some self-capacitanceembodiments, a single conductive trace to each electrode may be used asboth a drive and sense line.

In mutual capacitance systems, the “mutual” capacitance between a firstelectrode and a second electrode can be measured. In mutual capacitancesensing arrangements, the sensing points may be formed by the crossingsof patterned conductors forming spatially separated lines. For example,driving lines 105 a may be formed on a first layer and sensing lines 105b may be formed on a second layer 105 b such that the drive and senselines cross or “intersect” one another at sensing points 102. Thedifferent layers may be different substrates, different sides of thesame substrate, or the same side of a substrate with some dielectricseparation. Because the drive and sense lines are separated, there is acapacitive coupling node at each “intersection.”

The manner in which the drive and sense lines are arranged may vary. Forexample, in a Cartesian coordinate system (as illustrated), the drivelines may be formed as horizontal rows, while the sense lines may beformed as vertical columns (or vice versa), thus forming a plurality ofnodes that may be considered as having distinct x and y coordinates.Alternatively, in a polar coordinate system, the sense lines may be aplurality of concentric circles with the drive lines being radiallyextending lines (or vice versa), thus forming a plurality of nodes thatmay be considered as having distinct r and angle coordinates. In eithercase, drive lines 105 a may be connected to drive circuit 104, andsensing lines 105 b may be connected to sensing circuit 103.

During operation, a drive signal (e.g., a periodic voltage) is appliedto each drive line 105 a. When driven, the charge impressed on driveline 105 a can capacitively couple to the intersecting sense lines 105 bthrough nodes 102. This can cause a detectable, measurable currentand/or voltage in sense lines 105 b. The relationship between the drivesignal and the signal appearing on sense lines 105 b is a function ofthe capacitance coupling the drive and sense lines, which, as notedabove, may be affected by an object in proximity to node 102.Capacitance sensing circuit (or circuits) 103 may sense sensing lines105 b and may determine the capacitance at each node as described ingreater detail below.

As discussed above, conventional drive lines 105 a were driven one at atime, while the other drive lines were grounded. This process wasrepeated for each drive line 105 a until all the drive lines had beendriven, and a touch image (based on capacitance) was built from thesensed results. Once all the lines 105 a had been driven, the sequencewould repeat to build a series of touch images. However, in someembodiments of the present invention, multiple drive lines may be drivensimultaneously or nearly simultaneously, as described, for example,below. As used herein, “simultaneously” encompasses preciselysimultaneous as well as nearly simultaneous events. For example,simultaneous events may begin at about the same time, end at about thesame time, and/or take place over at least partially overlapping timeperiods.

FIG. 3 illustrates a simplified schematic diagram of mutual capacitancecircuit 300 corresponding to the arrangement described above. Mutualcapacitance circuit 300 may include drive line 105 a and sense line 105b, which are spatially separated thereby forming capacitive couplingnode 102. Drive line 105 a may be electrically (i.e., conductively)coupled to drive circuit 104 represented by voltage source 301. Senseline 105 b may be electrically coupled to capacitive sensing circuit103. Both drive line 105 a and sense line 105 b may, in some cases,include some parasitic capacitance 302.

As noted above, in the absence of a conductive object proximate theintersection of drive line 105 a and sense line 105 b, the capacitivecoupling at node 102 stays fairly constant. However, if an electricallyconductive object (for example, a user's finger, stylus, etc.) comes inproximity to node 102, the capacitive coupling (i.e., the capacitance ofthe local system) changes. The change in capacitive coupling changes thecurrent (and/or voltage) carried by sense line 105 b. Capacitancesensing circuit 103 may note the capacitance change and the position ofnode 102 and report this information in some form to processor 106 (FIG.1 ).

With reference to FIG. 1 , sensing circuit 103 may acquire data fromtouch surface 101 and supply the acquired data to processor 106. In someembodiments, sensing circuit 103 may be configured to send raw data(e.g., an array of capacitance values corresponding to each sense point102) to processor 106. In other embodiments, sensing circuit 103 may beconfigured to process the raw data itself and deliver processed touchdata to processor 106. In either case, the processor may then use thedata it receives to control operation of computer system 107 and/or oneor more applications running thereon. Various implementations alongthese lines are described in the applications referenced above, andinclude a variety of computer systems having touch pads and touchscreens.

In some embodiments, sensing circuit 103 may include one or moremicrocontrollers, each of which may monitor one or more sensing points102. The microcontrollers may be application specific integratedcircuits (ASICs), that work with firmware to monitor the signals fromtouch sensitive surface 101, process the monitored signals, and reportthis information to processor 106. The microcontrollers may also bedigital signal processors (DSPs). In some embodiments, sensing circuit103 may include one or more sensor ICs that measure the capacitance ineach sensing line 105 b and report measured values to processor 106 orto a host controller (not shown) in computer system 107. Any number ofsensor ICs may be used. For example, a sensor IC may be used for alllines, or multiple sensor ICs may be used for a single line or group oflines.

FIG. 4 illustrates at a high level process 400 for operating amulti-touch sensing arrangement, like that described above. The processmay begin at block 401 where plurality of sensing points 102 are driven.Following block 401, the process flow can proceed to block 402, wherethe outputs from sensing points 102 are read. For example, a capacitancevalue for each sensing point 102 can be obtained. Following block 402,the process can proceed to block 403 where an image or other form ofdata (signal or signals) of the touch at one moment in time can beproduced and thereafter analyzed to determine where objects touching orin proximity to the touch sensor may be located. Following block 403,the process can proceed to block 404, where the current image or signalmay be compared to one or more past images or signals to determine achange in one or more of the shape, size, location, direction, speed,acceleration, pressure, etc. for each object. This information can besubsequently used (in step 405) to perform an action in computer system107, ranging from moving a pointer or cursor to complex gesture-basedinteractions.

As noted above, enhanced operation of multi-touch sensing arrangementsmay be achieved by driving multiple rows simultaneously. An examplemulti-touch sensing device 500 with which multi-row stimulation may beemployed is illustrated in FIG. 5 and has reference numerals generallycorresponding to sensing arrangement 101 illustrated in FIG. 1 . In thegiven example, touch sensitive surface 501 has sixteen drive rows 505 a,although any number of drive rows could be used. The drive rows may bedivided, for example, into four groups, e.g., Group 1, Group 2, Group 3,and Group 4, each including four drive rows 505 a. Other numbers ofgroups and numbers of rows per group may also be employed.

Scanning of multi-touch sensor arrays is described in variousreferences, including U.S. patent application Ser. No. 11/381,313, whichis hereby incorporated by reference. The process may be brieflysummarized by reference to FIG. 7 . In general, a periodic waveform(e.g., a series of square wave pulses) is applied sequentially to driverows 505 a. For example, a first group of pulses 701 may be applied toRow A, followed by a second group of pulses 702 applied to row B,followed by a third group of pulses 703 applied to Row C, followed by afourth group of pulses 704 applied to Row D. These periodic waveformsare capacitively coupled into sense lines 505 b, generally resulting insensed waveform 705 on each sense line. Sensed waveform 705 can be inputintegrated over a predetermined time period to measure the capacitivecoupling between drive lines 505 a and sense lines 505 b at each node502. Other processing, such as filtering, demodulation, etc., may alsooccur.

In sensed waveform 7051 the time period from t₀ to t₁ corresponds to thestimulus of Row A. Integrating the sensed waveform over this time periodresults in a numerical value X1, which can correspond to the capacitanceof a node at the intersection of Row A and the column being sensed.Similarly, the time period from t₁ to t₂ corresponds to Row B, the timeperiod from t₂ to t₃ corresponds to Row C, and the time period from t₃to t₄ corresponds to Row D. Integrating the sensed waveform over each ofthese time periods can give numerical values X2, X3, and X4corresponding to the capacitance of nodes at the intersection of theRows B, C, and D and the column being sensed.

FIG. 8 illustrates a multi-line stimulation arrangement in which twolines may be stimulated simultaneously. Specifically, Row A and Row Bmay be simultaneously (or nearly simultaneously) stimulated withwaveforms 801 and 802. As can be seen, the phase of waveform 801 may beadjusted, e.g., after the fourth pulse. As a result, the remainingpulses of waveforms 801 and 802 may be 180° out of phase. Similarly, RowC and Row D may be simultaneously (or nearly simultaneously) stimulatedwith waveforms 806 and 807. Again, the phase of waveform 806 may beadjusted, e.g., after the fourth pulse. As a result, the remainingpulses of waveforms 806 and 807 may be 180° out of phase. The phaserelationships between the waveforms may be easily understood withreference to the + and − signs above.

Unlike the example described above with reference to FIG. 7 , the timeperiods t₀ to t₁, t₁ to t₂, t₂ to t₃, and t₃ to t₄ may no longeruniquely correspond to Rows A-D. Likewise, the measured values X1, X2,X3, and X4 resulting from integrating the sensed waveform (not shown)over these time periods no longer uniquely correspond to the capacitanceof a node at the intersection of a particular row and the column beingsensed. In the example of FIG. 8 , time periods t₀ to t₁ and t₁ to t₂,along with their corresponding measured values X1 and X2, correspondtogether to both Row A and Row B. Similarly, time periods t₂ to t₃ andt₃ to t₄, along with their corresponding measured values X3 and X4,correspond together to both Row C and Row D. However, because of thephase difference between the stimulus waveforms 801 and 802, the effectsof stimulating Row A only and Row B only can be isolated from eachother. Similarly, because of the phase difference between the stimuluswaveforms 806 and 807, the effects of stimulating Row C only and Row Donly can be isolated from each other.

Specifically, because stimulus waveforms 801 and 802 are in phase overtime period t₀ to t₁ and out of phase over time period t₁ to t₂ theintegration result X1 plus the integration result X2 (i.e., X1+X2) canyield a value corresponding to the capacitance of a node at theintersection of Row A and the line being sensed, i.e., only the effectof the stimulus of Row A. Similarly, the integration result X1 minus theintegration result X2 (i.e., X1−X2) can yield a value corresponding tothe capacitance of a node at the intersection of Row B and the linebeing sensed, i.e., only the effect of the stimulus of Row B.

The same applies to Rows C and D. Because stimulus waveforms 806 and 807are in phase over time period t₂ to t₃ and out of phase over time periodt₃ to t₄, the integration result X3 plus the integration result X4(i.e., X3+X4) can yield a value corresponding to the capacitance of anode at the intersection of Row C and the line being sensed, i.e., onlythe effect of the stimulus of Row C. Similarly, the integration resultX3 minus the demodulation result X4 (i.e., X3−X4) can yield a valuecorresponding to the capacitance of a node at the intersection of Row Dand the line being sensed, i.e., only the effect of the stimulus of RowD.

FIG. 9 illustrates an exemplary multi-line stimulation arrangement inwhich four lines are stimulated simultaneously. During a first periodfrom t₀ to t₁, the periodic waveforms 901-904 applied to Rows A-D are inphase. At time t₁, e.g., after the fourth pulse, the phase of waveforms901 and 902 can be adjusted so that waveforms 901 and 902 are 180° outof phase with respect to waveforms 903 and 904. Similarly at time t₂,e.g., after the next four pulses, the phases of waveforms 901 and 903are adjusted. This can result in waveforms 901 and 904 being 180° out ofphase with respect to waveforms 902 and 903. Finally, at time t₃, e.g.,after four more pulses, the phase of waveforms 901 and 902 can again beadjusted. This can result in waveforms 901 and 903 being 180° out ofphase with respect to waveforms 902 and 904. The phase relationshipsbetween the various waveforms can be understood with reference to the +and − signs in the figure.

As in the preceding example, the phase relationships between waveforms901-904 allow the effects of the stimulus on each individual row to beisolated as mathematical combinations of the measured integrationresults. Specifically, the effects of the stimulus of Row A can bedetermined by the expression X1+X2+X3+X4. The effects of the stimulus ofRow B can be determined by summing X1+X2−X3−X4. The effects of thestimulus of Row C can be determined by X1−X2−X3+X4. The effects of thestimulus of row D can be determined by X1−X2+X3−X4.

The process of operation 600 of the multi-touch sensing arrangement 500with multi-row stimulation may be further understood with reference tothe flow chart of FIG. 6 . First, the DC content for a group of rows canbe obtained 601. In the example of FIG. 8 , the DC content of the groupof rows including Rows A and B can be obtained by integrating the sensedwaveform over time period to t₀ to t₁. This DC content can indicate(somewhat coarsely) whether there is any touch present within a givengroup, e.g., Rows A and B, corresponding to a particular region of touchsurface 501. If at decision block 602, it is determined that there is notouch within a given group/region the next group (e.g., Rows C and D)can be similarly scanned. This may be implemented, for example, byimplementing counter 603. If at decision block 602, it is determinedthat there is touch within a given group/region as indicated by the DCcontent of the group, a fine scan of the group is performed in block604. The results of the fine scan may be combined to extract the signalscorresponding to each row as described above. Once all groups have beenscanned, the process repeats.

Turning back to FIGS. 5 and 6 , each group of rows may be scannedaccording to the principles described in the foregoing paragraphs. Amulti-touch sensing arrangement may comprise any number of rows and anynumber of groups. In some embodiments, a multi-touch sensing arrangementcan employ multi-line stimulation on a single group, i.e., all lines ofthe device may be stimulated simultaneously or nearly simultaneously.Additionally, although described in terms of rows and columns, the driveand sense lines may be arranged in any geometric arrangement.

Multi-line stimulation as described above may provide a number ofadvantages. For example, when multiple rows are stimulatedsimultaneously, the stimulus voltage can be reduced. Specifically, theadditive effect of multiple-row stimulus can result in the same sensedwaveform amplitude for a lower “per row” stimulus voltage. For example,a single-line scanning arrangement using an 18 Vpp (volts peak-to-peak)stimulus voltage could use a 9 Vpp stimulus voltage with two lines beingsimultaneously stimulated or with a 4.5 Vpp stimulus voltage with fourlines being simultaneously stimulated, etc., to obtain similar sensedwaveform amplitude.

Reducing the stimulus voltage can allow drive signals to be supplieddirectly from a driver chip without requiring a high voltage booster.The reduced voltage can also help to avoid fringe field and transistorbreakdown issues. The reduced voltage can also result in reduced powerconsumption. Because power scales as square of voltage, cutting voltageby a factor of four (for four row simultaneous stimulation) cuts thepower per row by a factor of 16. However, because there are four rowsbeing driven, the actual power savings may only be a factor of 4.However, additional power may also be saved by not doing a fine-scanwhen there is no touch detected during a DC scan of the region, asdescribed above.

A variation on the multi-row stimulation techniques described above maybe referred to as differential multi-row stimulation. Differentialmulti-row stimulation may be understood with reference to the tablebelow, which shows the polarities of the stimulating waveforms for themulti-row stimulation example of FIG. 9 above (Multi-Row Stimulation)compared to the polarities of the stimulating waveforms for adifferential multi-row stimulation example (Differential Multi-RowStimulation). Differential multi-row stimulation may generallycorrespond to the multi-row stimulation examples discussed above, exceptthat the polarities of the stimulating waveforms may be rearranged asindicated below.

Stimulus Voltage Phase Comparison Multi-Row Stimulation DifferentialMulti-Row Stimulation Row Row Row X1 X2 X3 X4 Sum Row X1 X2 X2 X4 Sum A + + + + +4 A − + − + 0 B  + + − −  0 B + + − − 0 C  + − − +  0 C + − +− 0 D  + − + −  0 D − − + + 0 Col. +4 0 0 0 Col. 0 0 0 0 Sum Sum

As can be seen from the table, in the multi-row stimulation example, thenet polarity applied across row A can have a DC component of four timesthe amplitude of the stimulus waveform. Similarly, the first time period(during which the value X1 may be measured) also can have a net DCcomponent of four times the amplitude of the stimulus waveform. In thedifferential multi-row stimulation example, the polarities may berearranged such that no row nor time period has a DC component. Theabsence of a DC component can result in a number of advantages,including allowing the charge sensing circuitry to operate with zerooffset, automatic baseline removal, inherent centroids computation, andincreased signal to noise ratio. In some embodiments, it may be desiredto stimulate all rows of the sensor simultaneously (i.e., have only onegroup of rows) as differences in DC offset from one group to another maybe lost because of an absence of DC content in the stimulus.

Other variations of the multi-row stimulation concept include phase orfrequency-based multi-row stimulation. In the foregoing examples,different rows can be stimulated with waveforms having polarity (phase)differences so that effects of a given row may be isolated in theaggregate sense waveform. Another way to allow this type of isolation,illustrated in FIG. 11 , is to stimulate each row of a group with astimulus waveform having a different frequency. One or more demodulationcircuits can then separate these frequencies in the sense waveform sothat the contributions of each stimulated line may be isolated. In manyembodiments demodulator circuits may already be present for noisefiltering.

Examples of other possibilities for stimulus waveforms according to theprinciples described herein may be understood with reference to FIG. 12. Timing signal 1201 can define a stimulus time window. Each line canhave a corresponding timing signal. During the stimulus time window,e.g., when signal 1201 is high, a stimulation waveform can be applied tothe corresponding line (or lines). This stimulation waveform may take avariety of forms, including a square wave, a sine wave, an exponentiallydecaying sine wave, a pulsed sine wave, etc.

Simultaneous stimulation, as used herein, means that at least onestimulus is applied to at least two lines during the same time period(e.g., window, which can include one or more pulses of any shape and inany combination). In other words, simultaneous stimulation involves atleast two lines having stimulus windows that at least partially overlapin time. For example, in FIG. 12B, a stimulus window for Row A, definedby timing signal 1201 a can begin at the same time, extend for the sameduration, and end at the same time as a stimulus window for Row B,defined by timing signal 1201 b. Alternatively, as illustrated in FIG.12C, the stimulus windows for Row A (defined by timing signal 1201 a)and Row B (defined by timing signal 1201 b) may begin and end atdifferent times, but have at least some overlapping portion. Anotheralternative, illustrated in FIG. 12D, is for stimulus windows for Row A(defined by timing signal 1201 a) and Row B (defined by timing signal1201 b) may begin at the same time, but end at different times. Stillanother alternative, illustrated in FIG. 12E, is for stimulus windowsfor Row A (defined by timing signal 1201 a) and Row B (defined by timingsignal 1201 b) to begin at different times but end at the same time.These various arrangements can also be extended to a number of rowsgreater than two, with complete flexibility so long as there is somestimulation overlap between at least some rows.

The principles described herein may be used to devise input devices fora variety of electronic devices and computer systems. These electronicdevices and computer system may be any of a variety of types illustratedin FIG. 10 , including desktop computers 1001, notebook computers 1002,tablet computers 1003, handheld computers 1004, personal digitalassistants 1005, media players 1006, mobile telephones 1007, and thelike. Additionally, the electronic devices and computer systems may becombinations of these types, for example, a device that is a combinationof a personal digital assistant, media player, and mobile telephone.

Other alternations, permutations, and combinations of the aforementionedembodiments are also possible. For example, multiple touch and proximitysystems may be designed based on infrared/optical sensing arrangementsthat rely on periodic waveform stimulus and reflections from hand partsor other touch objects to detect touch and/or hover events. Theprinciples herein, though described with reference to capacitivesystems, are equally applicable to any systems in which touch orproximity sensing depends on information extracted from periodicstimulus waveforms. It is therefore intended that the following claimsbe interpreted as including all alterations, permutations, combinationsand equivalents of the foregoing.

The invention claimed is:
 1. A method of driving a touch sensitivesurface, the touch sensitive surface comprising a plurality of sensingpoints, each sensing point being associated with at least one of aplurality of drive lines and at least one of a plurality of sense lines,the method comprising: simultaneously stimulating the plurality of drivelines during each of a plurality of time periods with an equal number ofin-phase and out-of-phase stimulus waveforms such that a net DCcomponent of a sense signal on each of the plurality of sense lines ineach of the plurality of time periods is about zero volts.
 2. The methodof claim 1, further comprising simultaneously stimulating the pluralityof drive lines during the plurality of time periods such that the net DCcomponent on each of the plurality of drive lines over the plurality oftime periods is about zero volts.
 3. The method of claim 1, furthercomprising simultaneously stimulating at least one of the plurality ofdrive lines during the plurality of time periods with differentpolarities of a stimulus waveform such that the net DC component on theat least one drive line over the plurality of time periods is about zerovolts.
 4. The method of claim 3, further comprising simultaneouslystimulating at least one of the plurality of drive lines during theplurality of time periods with different polarities of the stimuluswaveform by changing a phase of the stimulus waveform over the pluralityof time periods.
 5. The method of claim 1, further comprisingsimultaneously stimulating two or more drive lines of the plurality ofdrive lines during the plurality of time periods with differentpolarities of a stimulus waveform such that the net DC component of thetwo or more drive lines during any one of the plurality of time periodsis about zero volts.
 6. The method of claim 1, further comprisingsimultaneously stimulating two or more drive lines of the plurality ofdrive lines during the plurality of time periods with differentpolarities of a stimulus waveform such that the net DC component of thetwo or more drive lines after all of the plurality of time periods haveelapsed is about zero volts.
 7. The method of claim 1, furthercomprising: sensing the sense signal on at least one of the plurality ofsense lines, wherein the sense signal is related to the plurality ofdrive lines by touch or proximity of one or more objects at one or moreof the plurality of sensing points associated with the plurality ofdrive lines and the at least one sense line; deriving a plurality ofvalues from the sense signal; and deriving touch information from amathematical combination of the plurality of values.
 8. The method ofclaim 7, wherein deriving the plurality of values from the sense signalcomprises integrating the sense signal over time.
 9. The method of claim1, wherein the plurality of drive lines are simultaneously stimulatedduring the plurality of time periods with drive signals of a samefrequency, wherein a first half of two or more drive signals are out ofphase with a second half of the two or more drive signals during atleast one of the plurality of time periods.
 10. The method of claim 1wherein a predetermined phase relationship of drive signals applied tothe plurality of drive lines is selected to eliminate the net DCcomponent of the sense signal.
 11. A touch sensing device comprising: atouch sensitive surface having a plurality of sensing points, eachsensing point being associated with one of a plurality of drive linesand one of a plurality of sense lines; and drive circuitry coupled tothe plurality of drive lines, the drive circuitry configured forsimultaneously stimulating the plurality of drive lines during each of aplurality of time periods with an equal number of in-phase andout-of-phase stimulus waveforms such that a net DC component of a sensesignal on each of the plurality of sense lines in each of the pluralityof time periods is about zero volts.
 12. The touch sensing device ofclaim 11, the drive circuitry further configured for simultaneouslystimulating the plurality of drive lines during the plurality of timeperiods such that the net DC component on each of the plurality of drivelines over the plurality of time periods is about zero volts.
 13. Thetouch sensing device of claim 11, the drive circuitry further configuredfor simultaneously stimulating at least one of the plurality of drivelines during the plurality of time periods with different polarities ofa stimulus waveform such that the net DC component on the at least onedrive line over the plurality of time periods is about zero volts. 14.The touch sensing device of claim 11, the drive circuitry furtherconfigured for simultaneously stimulating at least one of the pluralityof drive lines during the plurality of time periods with differentpolarities of a stimulus waveform by changing a phase of the stimuluswaveform over the plurality of time periods.
 15. The touch sensingdevice of claim 11, further comprising sense circuitry coupled to theplurality of sense lines, the sense circuitry configured to: sense thesense signal on at least one of the plurality of sense lines, whereinthe sense signal is related to the plurality of drive lines by touch orproximity of one or more objects at one or more of the plurality ofsensing points associated with the plurality of drive lines and the atleast one sense line; derive a plurality of values from the sensesignal; and derive touch information from a mathematical combination ofthe plurality of values.
 16. The touch sensing device of claim 15,wherein deriving the plurality of values from the sense signal comprisesintegrating the sense signal over time.
 17. A touch sensing devicecomprising: a touch sensitive surface having a plurality of sensingpoints, each sensing point being associated with one of a plurality ofdrive lines and one of a plurality of sense lines; and drive circuitrycoupled to the plurality of drive lines, the drive circuitry configuredfor simultaneously stimulating the plurality of drive lines during aplurality of time periods to achieve an absence of a DC component of asense signal on each of the plurality of sense lines in each of theplurality of time periods.
 18. The touch sensing device of claim 17, thedrive circuitry further configured for simultaneously stimulating theplurality of drive lines during the plurality of time periods to achievean absence of the DC component on each of the plurality of drive linesover the plurality of time periods.
 19. The touch sensing device ofclaim 17, further comprising sense circuitry coupled to the plurality ofsense lines, the sense circuitry configured to: sense the sense signalon at least one of the plurality of sense lines, wherein the sensesignal is related to the plurality of drive lines by touch or proximityof one or more objects at one or more of the plurality of sensing pointsassociated with the plurality of drive lines and the at least one senseline; derive a plurality of values from the sense signal; and derivetouch information from a mathematical combination of the plurality ofvalues.
 20. The touch sensing device of claim 19, wherein deriving theplurality of values from the sense signal comprises integrating thesense signal over time.